EMD SD90MAC

The EMD SD90MAC is a 6250 horsepower (4.5 MW) C-C diesel-electric locomotive produced by General Motors Electro-Motive Division. It is, with the SD80MAC, one of the largest single-engined locomotives produced by that company, surpassed only by the dual-engined DD series. The SD90MACs feature radial steering trucks and an isolated cab which is mounted on shock absorbers to lessen vibrations in the cab. All SD90MACs use AC traction motor technology. They are all hood units fitted with safety cabs. The SD90MAC, like the SD80MAC, SD70ACe, and SD70M-2, has a wide radiator section, nearly the entire width of the locomotive, which along with their size makes them easy to spot.

History

The SD90MAC was introduced in 1995, along with the SD80MAC locomotives. The SD90MAC was designed to utilized the new 16-cylinder H-engine, while the SD80MAC was designed to use the 20 cylinder version of the existing 710G engine. However, technical problems with the engine resulted in the first locomotives being shipped with 4300 horsepower (3.2 MW) 16-cylinder 710G motors, making them similar to the SD70MACs. These locomotives were given the model SD90/43MAC and railroads were given the option to remotor them with 6250 horsepower (4.5 MW) engines when they became available. This upgrade program was rarely used due to reliability issues with the newer engine. Over 400 SD90/43MAC locomotives were built.

In 1996, EMD entered full production on their 6250 horsepower (4.5 MW), 16-cylinder H-engine, and all SD90MACs made from then on used that for its prime mover. Locomotives fitted with this engine are sometimes referred to as SD90MAC-H locomotives. Later versions of the SD90MAC-H feature a Phase II cab, with a new nose which offers higher visibility from the cab than the old nose. The SD90MAC-H did not prove popular with railroads and less than 70 were built, including EMD demonstrator units. Since the SD90MAC-H had such a large prime mover, it didn't offer the same operational flexibility as smaller units, limiting its possible customer base to only the largest railroads. Also, since the H-engine was a new design it hadn't reached the same level of reliability as EMD's previous engine. The low reliability on such a large engine was an especially bad combination since the loss of one engine in a train meant the loss of a larger percentage of pulling power than had a smaller engine failed. In the end the SD90MAC-H was only delivered to two railroads, the Union Pacific Railroad and the Canadian Pacific Railway. The Canadian Pacific locomotives were part of an earlier order for SD90/43MAC locomotives that was still in production when EMD switched over to the H-engine.

EMD also tried offering a lower-power version of the SD90MAC with a 12-cylinder engine called the SD89MAC, but none were produced other than the prototype.

Current status

As of January 2005, the SD90MAC is no longer in production due to the Environmental Protection Agency's Tier 2 locomotive emission regulations, although EMD may be able to get the H-engine approved at some later date. However, the People's Republic of China recently announced an order for 300 JT56ACe locomotives, which also use the H-Engine as its prime mover. A portion of the locomotives will be assembled in kit form by China's own Dalian Locomotive Works. These units were reportedly capable of meeting the EPA's strict regulations and began delivery in the latter half of 2007.

Update

On August 1, 2008 Union Pacific Railroad announced that it would be retiring 21 of the SD90MAC locomotives. According to sources common parts will be used to maintain the railroads 710-engined SD9043MAC fleet. The 265H prime mover will be cut up or exported. The only part that is non-reuseable will be the frame. These units, in the 8900 series will be pulled from the dead line in Denver, and be sent to East St. Louis, Ill., in small batches to be dismantled. (cited: Trains magazine online)

See also

• GE AC6000CW An equally powerful locomotive built by GE that entered production soon after the SD90MAC. These also suffered from engine problems and some were also sold with less powerful engines. GE also offered upgrades, but none were performed. As of Oct 2008, the AC6000CW engines were still in use, in particular Union Pacific's 75xx series.

References

• The Locomotive Place. Retrieved on January 13, 2005.
• The Unofficial EMD homepage. Retrieved on January 13, 2005.